Molecular beam epitaxy (MBE) may be used to deposit metal and semiconductor compounds onto substrates such as silicon so as to form infrared and visible light affecting matrixes. A process to do this is disclosed in patent application Ser. No. 07/524,959, filed May 18, 1990 by one of the inventors of the present application, Robert W. Fathauer. The teachings of this prior patent are incorporated herein by reference.
In the process of the above referenced patent, molecules of a vaporized material are directed onto the surface of a substrate at a selected rate. The arriving molecules remain mobile on the surface for a short time. Thus, each molecule has time to locate a preferred site upon which to attach so that a regular crystal growth is facilitated. Column like structures grow epitaxially up from the substrate surface. The orientation, height, width, shape, and spacing of the columns are all selectable by modification of the processing parameters rather than by masking. A large variety of desired three dimensional shapes may be generated. Specifically, the above referenced patent discloses that metal and silicon are deposited onto a silicon substrate in ratios well removed from stoichiometric with a large excess of silicon. Given the correct growth environment, columns of single crystal metal silicide epitaxially grow upward from the silicon substrate surface. The columns are embedded in a surrounding matrix of single crystal silicon. It has been determined that the spacing, thickness, and height of the columns may be chosen by varying the process parameters. Alternatively, the location and shape of the columns may be selected by seeding the substrate in the places where columns are desired.
If the deposited metal is cobalt, cobalt disilicide columns are formed. Other metals or even semiconductors may be used, but cobalt disilicide is an effective and well understood material. When photons strike metal silicides like cobalt disilicide, they may be absorbed. The above referenced patent teaches a structure to maximize this absorption effect in which many short column like particles of silicide are grown inside a matrix of silicon to produce a three dimensional cloud of silicide particles that is more likely to intercept photons. The present invention improves upon this structure by producing silicide particles that can be tailored to interact with selected wavelengths of light in a linear or non-linear manner.